关闭/重新启动期间无法发送Unix邮件

Question

We have a perl script which tries to send an email notification when the system is about to shut down. To do this, we catch the SIGTERM and call Unix mail command to send email in the signal handler. SIGTERM is caught but the unix mail log shows that the FROM and TO address are changed from user@companyname.com to user@hostname during shutdown. Any idea why the system does this and how to prevent it? (Please note: The same email works fine when we run the script and kill the process from terminal)

Here is the perl code snippet:

$SIG{TERM} = \&signal_handler;

sleep(3600);

sub signal_handler { 

my $email_address = 'user@companyname.com';

system("echo \"TestBody\" | mail -s \"TestEmailSubject\" -c \"$email_address\" -r \"$email_address\" \"$email_address\"");

}

Here is what is printed in /var/log/mail/mail during shutdown:

Sep 17 21:17:04 postfix/postfix-script[7009]: starting the Postfix mail system

Sep 17 21:17:10 postfix/master[7011]: daemon started -- version 2.10.1, configuration /etc/postfix

Sep 17 21:17:10 postfix/pickup[10349]: 35F801809C9: uid=0 from=root

Sep 17 21:17:10 postfix/cleanup[10356]: 35F801809C9: message-id=<20190917211710.35F801809C9@HOSTNAME.net>

Sep 17 21:17:10 postfix/qmgr[10350]: 35F801809C9: from=root@HOSTNAME.net, size=1618, nrcpt=1 (queue active)

Sep 17 21:17:10 postfix/local[10372]: 35F801809C9: to=root@HOSTNAME.net, orig_to=<root>, relay=local, delay=13, delays=13/0.01/0/0, dsn=2.0.0, status=sent (delivered to file: /dev/null)

Here is the working case when we kill the process from terminal:

Sep 17 21:20:41 postfix/pickup[10349]: E5328180968: uid=14936 from=user@COMPANYNAME.com

Sep 17 21:20:41 postfix/cleanup[22690]: E5328180968: message-id=<5d814e29.qZd+wgg47afpUdbd%user@COMPANYNAME.com>

Sep 17 21:20:41 postfix/qmgr[10350]: E5328180968: from=user@COMPANYNAME.com, size=544, nrcpt=1 (queue active)

Sep 17 21:20:41 postfix/smtp[22692]: E5328180968: to=user@COMPANYNAME.com, delay=0.06, delays=0.01/0/0/0.05, dsn=2.0.0, status=sent (250 2.0.0 OK 4E/77-59832-92E418D5)

Answer 1

the postfix system is probably being shut down earlier in the shutdown process than your script. Have you confirmed within your script that the mail system is still up after your script has tried to send an email?